Marble is a crystalline rock which, if pure, would be composed entirely of carbonate of lime (calcium carbonate, CaCo.sub.3, the original material of limestone). It is a rock valued for its beauty and is widely used for making statuary and monuments, for architectural treatment in construction, and for ornamentation. Many limestones which become decorative when polished are also termed marbles. Limestone assumes a bewildering number of widely divergent physical forms, including marble, travertine, chalk, etc. Limestone is also generally classified in the following types: "high calcium", in which the carbonate content is essentially calcium carbonate with no more than 5 percent magnesium carbonate (usually less); "magnesian", which contains both carbonates, with a magnesium carbonate content of about 5 to 20 percent; and "dolomitic", which contains over 20 percent magnesium carbonate but not more than 45.6 percent magnesium carbonate, with the balance calcium carbonate. Individual limestone types are further described by many common names, as detailed in Kirk & Othmer, Encyclopedia of Chemical Technology. Third Edition, Vol. 14, John Wiley & Sons (1981), pages 343- 352.
Marble is a common term for a metamorphic, highly crystalline rock that may be high-calcium or dolomitic limestone of varying purity. It occurs in virtually every color in diverse mottled effects and is the most beautiful form of limestone. It is usually very hard and can be cut and polished to a very smooth surface.
It is known that calcium carbonate-containing stone surfaces, such as marble floors, may be maintained in a variety of ways. It is convenient to identify three categories of treatment: (1) polishing or crystallizing (vitrification) of the stone surface with a pad of material, usually in combination with polishing agents; (2) application of chemicals which penetrate the stone surface, thereby sealing it against staining and, hopefully, improving its appearance, followed by or combined with polishing of the sealed stone surface; and (3) application of film-forming compositions to the stone surface to seal and protect it from staining and abrasion. In the latter method, polishing of the film surface is typically part of the maintenance procedure. This invention relates to treating the stone surface, as in (1) above, with novel nonwoven abrasives. Although a marble floor is used herein to exemplify the calcium carbonate-containing stone surface, the invention is applicable to calcium carbonate-containing stone surfaces in general.
The gloss produced by buffing a marble floor with an abrasive article attached to a conventional rotary floor machine depends on a number of factors. Among these are the type of abrasive article employed, the nature and amount of ancillary chemical used (if at all) with the abrasive article, the pressure applied to the floor, the speed of rotation of the abrasive article, the treatment time at given pressure, etc. To ensure acceptable gloss production as a result of the treatment procedure,.the user tries to optimize all of these parameters. The goal is a high gloss, high durability, stain resistant floor, achieved with a minimum of labor.
A newly installed marble floor is typically honed with coarse abrasives followed by a series of increasingly finer abrading materials in order to smooth the originally installed floor, to remove lippage, and eventually to produce a smooth, level surface with a satin sheen. Further mechanical polishing with increasingly finer grades of diamond abrasives will ultimately yield a very high gloss.
A honed floor requires only dusting and wet-mopping to maintain its appearance. However, a honed marble floor will have little or no resistance to staining insofar as the surface is naturally porous and no protective coating has been applied. In addition, the appearance of the honed floor, as indicated by "shininess", or "gloss", will typically be low. Even if the floor has been further polished with diamond abrasives to produce a very high gloss, the surface of the marble is still subject to rapid deterioration of gloss due to the abrasion of foot or other traffic, and the stain resistance of the surface is not improved.
In one traditional method of treating marble to achieve higher gloss and durability, an acid-containing composition is buffed onto the marble using a weighted rotary floor machine under which has affixed thereto a buffing pad comprising steel wool. This method is commonly referred to as "crystallization" or "vitrification" of the surface (the former sometimes being associated with the use of a fluorosilicate salt in the acidic composition). It is generally believed by those skilled in the art that the interaction of the acid, steel wool, and pressure-generated frictional heat from the weighted machine combine to alter the chemical composition of the marble surface to produce a harder and therefore more durable surface: one which can be polished to a higher gloss, and one which has improved stain resistance.
Batiment Entretien, "Brilliant Marble: is it easy to obtain? "]Jan-Feb, 1990 (English translation from French publication) states "Thus it is that, by the intermediary of an acid and a catalyst (iron), a physico-chemical reaction transforms the calcium carbonate into calcium fluoride and magnesium fluoride." This publication also describes in detail the process and equipment necessary to prepare and crystallize marble floors including steel wool pads and ancillary abrasive agents. Batiment Entretien, "Crystallization of Marble Stone," Jan-Feb, 1985, (English translation from French publication) is an earlier version of the same publication and it makes the same statements with respect to the necessity of steel wool for crystallizing the floor.
"Instrucciones Generales Para Cristalizar con Maquinas Y Productos Kleever", instructions for crystallizing marble floors (partially translated from Spanish), publication date unknown by Coor & Kleever S.A., Barcelona, Spain, states that steel wool is "indispensable" for use with its crystallizing agent (page 6), and other materials will not produce good results.
U.S. Pat. No. 4,738,876 (George, et al.), refers to a two-step crystallization method which comprises applying an acid conditioning composition as a primer with a "stripping grade pad", followed by application of a hexafluorosilicate salt crystallizing agent which is preferably applied and buffed with a wire wool (steel wool) pad in (column 6, line 57).
U.S. Pat. No. 4,756,766 (Thrower) describes a coating, cleaning, and conditioning process for marble which includes the use of a fluorosilicate composition and preferably a steel wool pad (column 2, lines 25-68 to column 3, lines 1-30). This reference also includes some postulated chemistry.
Hoechst Celanese Corp. (Somerville, N.J.), in a publication entitled "Bulletin: Vitrification Treatment for Stone Floors Formula JS 342/9", (published 1988), describes vitrification as "a one step procedure for the polishing of marble... floors." The vitrification formula known under the trade designation "JS 342/9" as described in the bulletin comprises a wax, a surfactant, an aluminum salt, an organic acid, and water. The vitrification formula is recommended to be buffed onto the floor with a low-speed machine (150 rpm) and a steel wool pad. Hoechst Celanese Corp. publication "Floor Polish Bulletin: Crystallization Treatment for Stone Floors, Formulation FA 1401", (published 1985), describes crystallization as "a one step procedure for polishing marble, terrazzo and hydraulic mosaic stone floors." The formulation comprises a water dispersion of magnesium silicofluoride, a surfactant, a nonyphenol with 10 moles of ethylene oxide, an organic acid, and a wax. The composition is to be buffed onto the floor with a steel wool pad.
Another cleaning industry publication, "Raising Standards for the 90's", Cleaning & Maintenance Magazine; June 1990, p.10, describes the use of wire wool pads with vitrification chemicals. Additionally, the technical literature of several major marble floor maintenance supply companies specify that steel wool pads be used with their treatment chemicals.
The use of steel or other wire wool pads has several disadvantages in marble maintenance. Slivers of steel wool shred from the pad during use and remain on the floor unless removed. These slivers quickly rust, discoloring the floor. Unless they are quickly and completely removed from the floor after the polishing procedure has been accomplished, rust spots will form, a particularly problematic stain on marble. Once the steel wool pad has been used, it also begins to rust and therefore cannot be stored for future use. Steel wool can be difficult to handle insofar as it tends to leave slivers in the skin of those handling it (in many cases, the pads are hand-made by the user from steel wool stock); and when in use as a pad on the floor, it tends to ball up or pull apart thus rendering the pad unfit for continued polishing even though much of the original steel wool remains on the pad. This tendency to shred, ball up, and pull apart is greater with finer (less lofty, more dense) grades of steel wool. Because of this, even though the finer grades of steel wool (such as #0000 or #00) are expected to produce a more brilliant gloss on the floor, typically the medium or fine grades (such as #0 or #1) are recommended for use in maintaining marble floors. U.S. Pat. No. 2,958,293 (Hoover, et al.) discusses the use and disadvantages of steel wool pads quite adequately.
Attempts have been made to improve on steel wool pads. For example, stainless steel wool pads have been used in order to prevent or retard rusting of the pad. Stainless steel wool pads, however, are more expensive than plain carbon steel wool pads, are no less difficult to handle, and have the same tendency to shred or ball up in use.
French patent application 88 02995 (Philippeau, published Sep. 4, 1989) describes an improved pad made from woven stainless steel fibers to be used for polishing marble.
U.S. Pat. No. 4,176,420 (Magid) describes a pad made from a continuous ribbon of stainless steel which is used for routine floor maintenance and which eliminates rusting, shredding, and linting associated with steel wool pads. No utility with respect to marble is taught or suggested.
In another known class of methods of treating marble, a liquid acid composition and a particulate abrasive material are mixed to form a slurry and slurried onto the floor. Polishing is accomplished by buffing the slurry onto the floor with a rotary floor machine to effect simultaneously a polishing action and a slight dissolution of the calcium carbonate in the marble by the acid in order to produce a smooth, high gloss surface. Pads used in this class of methods traditionally have been made of a number of materials including felts and pads made from synthetic nonwoven fibers.
U.S. Pat. No. 4,738,876, mentioned above, in disclosing a two-step process for crystallizing stone floors, refers to the use of an abrasive synthetic pad for application of the primer (claim 15). Review of the specification does not reveal a specific synthetic fiber for the abrasive synthetic pad, referring only to "black", "tan", and other color abrasive synthetic pads (Examples). Patentees admit that the pad composition is a non-critical aspect of their invention (column 6, lines 12-14).
U.S. Pat. No. 4,756,766, also mentioned above, describes a cleaning step using an abrasive composition buffed into the floor with a nylon pad (column 2, line 5).
U.S. Pat. No. 4,898,598 (Zapata) refers to the use of a "felt" pad for polishing marble in conjunction with a polishing compound (column 4, line 34). No specifics are given as to the composition of the felt.
One disadvantage of the slurry procedures is that the slurry can be spattered onto surrounding surfaces, such as walls and baseboards, by the rotating pad of the floor machine, creating an undesirable task of having to wipe clean the spattered slurry from walls and baseboards. Another disadvantage is that the pad may become clogged with the abrasive slurry and detritus from the floor, which may result in diminished abrasive effectiveness on the floor. Yet another disadvantage is that the proper amount of abrasive slurry must be maintained on the floor for proper polishing action even though the slurry is being moved away from the area intended to be polished by the rotary motion of the pad.
Uniform, lofty, open, nonwoven three-dimensional abrasive articles are known for use in cleaning and polishing floors and other surfaces. Examples of such nonwoven surface treating articles are the nonwoven abrasive pads made according to the teachings of Hoover, et al., mentioned above; McAvoy, U.S. Pat. No. 3,537,121; and McAvoy, et al., U.S. Pat No. 4,893,439. Hoover et al. describe such nonwoven pads as comprising
many interlaced randomly disposed flexible durable tough organic fibers which exhibit substantial resiliency and strength upon prolonged subjection to water and oils. Fibers of the web are firmly bonded together at points where they intersect and contact one another by globules of an organic binder, thereby forming a three-dimensionally integrated structure. Distributed within the web and firmly adhered by binder globules at variously spaced points along the fibers are abrasive particles.
Hoover, et al., at column 2, lines 61-70, column 3, line 1.
These nonwoven pads have been and are available in a wide range of abrasive quality from very coarse pads for gross removal of surface treatments (stripping or scouring pads containing, for example, as in Example I of Hoover, et al., 180 grit silicon carbide abrasive particles) to very finely abrasive or nonabrasive polishing pads (containing, for example, as in Example II of Hoover, et. al., 180 grit and finer flint fines, applied at about half the weight of the silicon carbide of Example I).
McAvoy, et al. '439 note that the abrasive particle grade can range from about 36 to about 1000, depending on the application. According to "American National Standard for Grading of Certain Abrasive Grain on Coated Abrasive Material" (ANSI ASC B74.18-1984), grade 36 corresponds to a screen aperture size of about 800 micrometers. The highest grade (smallest screen aperture size) given in the standard is grade 220, which has a "fines" sieve size listed as 64 micrometers. Particles corresponding to grade 1000 are apparently much smaller in size, having average particle diameter of about 10 micrometers. McAvoy, et al., do not, however, mention any abrasive particle size as critical within the range of 36 to 1000 grade abrasive particles, and do not teach or suggest which grades are preferred for maintaining various floor compositions.
U.S. Pat. No. 5,030,496 (McGurran) describes non-woven fibrous surface treating articles. As noted in column 5 , lines 61-68, useful abrasive particles may range in size anywhere from about 24 grade, average particle diameter of about 0.71 mm (or 710 micrometers), to about 1,000 grade, average particle diameter of about 0.0 mm (i.e., about 10 micrometers). No criticality is given to the average particle diameter nor is any attention given to crystallizing marble or other calcium carbonate-containing surfaces.
U.S. Pat. No. 5,082,720 (Hayes) describes melt-bondable fibers for use in nonwoven webs, including nonwoven abrasive webs which may include abrasive grains having grade ranging from about 36 to about 1000. However, as with the Hoover, et al., and McAvoy, et al., and McGurran patents no criticality is given to abrasive particle size or crystallization of calcium carbonate-containing surfaces.
Nonwoven abrasive pads such as disclosed by Hoover, et al., and McAvoy, et al., and McGurran, while finding wide ranging use, by themselves have not been suitable for polishing or crystallizing marble floors. This is clear from the continued and persistent use of non-abrasive-filled nonwoven pads in combination with an ancillary abrasive agents (such as abrasive slurries) for polishing marble, or the use of steel wool pads alone for crystallizing marble floors by those skilled in the art of marble floor maintenance.
Thus it was surprising to find that the articles of the present invention, comprising a uniform, lofty, open, nonwoven three-dimensional web, having very fine abrasive particles adhered to many interlaced randomly disposed flexible durable tough organic fibers, when used with ancillary acidic crystallization agents, crystallized marble and other calcium carbonate-containing surfaces equally or better than previously known materials, without the aforementioned problems associated with steel wool pads. A further advantage is that a high gloss may be obtained faster with the systems of the present invention than with systems known in the art, thus reducing the amount of labor required to achieve the desired appearance level of the marble system. Another advantage is that the nonwoven surface treating articles of the present invention contain no ferrous metal component: they will not shred into fine pieces and rust on the floor, nor will they rust during storage after having been used.